The success of fusion power requires alloys with good mechanical properties and the ability to withstand extreme thermal and irradiation conditions without prohibitive levels of activation or structural degradation. Body centred cubic multi-principal component alloys, V-Cr-Mn and Ti-V-Cr-Mn have shown promising high temperature stability at 1200 C. For the alloys to be suitable for use in nuclear fusion reactors, they must be stable across a wide range of temperatures relevant to fusion applications. Here, we assess alloy microstructural stability in these systems following long-term heat treatments at various temperatures. Encouragingly, most of the alloys showed no significant change in microstructure across all temperatures. This contrasts with many other multi-principal component alloys, which develop complex microstructures after exposure to intermediate temperatures.